Wave guide with phase compensating paired bends



Patented Jan. 10, 1950 WAVE GUIDE WITH PHASE COMPENSATING PAIRED BENDSWarren A. Tyrrell, Fail-haven, N. J assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication January 25, 1944, Serial No. 519,595

Claims.

The present invention relates to the guided transmission of ultra-highfrequency electromagnetic waves, and it has as its principal objectivethe elimination or substantial reduction of .undesirable efiects thatare incident to changes in the direction of the wave guiding structure.

In accordance with a feature of the invention a desired change in thedirection of the wave guide is effected, not by means of a single bend,but by a succession of differently oriented bends. In one embodiment,for example, a change of 90 degrees in the course of a hollow-pipe guideis provided by a pair of successive right angle bends disposed inmutually perpendicular planes.

The nature of the invention and its various features, objects andadvantages will appear more fully from a consideration of the followingdetailed description of the embodiments that are illustrated in theaccompanying drawing. In the latter, Figs. 1 to 3 illustrate how a90-degree change in direction may be accomplished in accordance with theinvention, and Fig. 4 shows diagrammatically a radio system embodyingthe invention.

In the arrangement illustrated in Fig. 1, the wave guiding structure isa hollow-pipe guide of circular cross-section. The guide comprises atubular shell of copper or other conducting material enclosing a lowloss dielectric medium, which may be air, for specific example, or anyother suitable non-conducting material. It is well known thatelectromagnetic waves can be propagated through the interior of such aguide provided the wave frequency exceeds a-critical or cut-offfrequency that is dependent on the internal diameter of the pipe, thedielectric coeflicient of the dielectric medium, and the type or fieldconfiguration of the waves. It may be assumed, in the interest of acomplete disclosure, of a specific embodiment, that the internal diam-;

eter of the pipe is 2% inches, thatthe dielectric medium is air, andthat the free-space wavelength of the guided waves is 9.80 centimeters,corresponding to a wave frequency of somewhat more than 3000 megacyclesper second. Under these circumstances the guide will support waves ofthe dominant or H11 type, that is, a non-symmetric type of transverseelectric wave in which the lines of electromotive force extend acrossthe interior of the pipe approximately parallel to a diameter.

The guide is represented in Fig. 1 as having a pair of adjacent -degreearcuate bends. The

lower bend l0 connects a guide section II, which leads to a source ofH11 waves, not shown, and

a short guide section I 2. The latter is connected in turn by the upperbend l3 to a guide section l4 which leads to a wave receiver, antenna orother utilization means, not shown. Referring to the indicated axes of asystem of rectangular coordinates, bend l0 and the guide sectionsconnected thereto lie in the YZ plane, while bend l3 and the guidesections connected thereto lie in a plane XY that is normal to theother. The two main guide sections II and I4, it will be noted, areoffset from each other by the distance L.

One of the undesirable effects that is introduced by a bend in a pipeguide of circular crosssection is ellipticity of polarization of thetransmitted waves. of dominant type transmitted through a bend in theguide is generally split into two mutually perpendicular components, onecomponent lying in the plane of the bend and the other componentperpendicular thereto, and that the two components travel with unequalvelocities. Hence, upon emerging from the bend, one component lags theother by an appreciable part of a wavelength, or, in other words, thetwo are displaced in phase angle. Excepting then for the possibilitythat the phase displacement may be degrees or a multiple thereof, theemergent waves are elliptically polarized. The usual wave receiver orother utilization means is ill adapted for elliptically polarized wavesbut is designed rather to utilize eificiently only plane polarized Waveshaving a predetermined fixed orientation. A typical receiver of H11waves, for example, comprises a diametral pick-up conductor so orientedin the guide that it is in registry with the electric field of theincident waves, the latter being a condition that cannot be maintainedif the incident waves are elliptically polarized. In addition to, oraside from, loss of efficiency other eflects produced by ellipticalpolarization of the transmitted waves may be regarded as deleterious inparticular systems.

Fig. 2 represents diagrammatically two wave components appearing in theintermediate guide section l2 as a result of the effect of bend I0- onplane polarized waves of dominant type applied through guide section II.The larger component a lies in the YZ plane and the smaller component blies at right angles thereto in the XY plane. Experimental studiesindicate that if the electric vector of the applied waves lies in the YZplane, i. e., in the plane of the bend,

component b is zero, and that if the electric Y I vector is rotated 90degrees, component a is zero,

It has been found that a wave is not represented in the drawing. In thespecific. .10

embodiment described with reference to Fig. 1 in which, it may befurther specified;thersmean; radius of curvature of the bends is 3inchesgxar. phase displacement of 25 degrees has been.found.

In another embodiment in Whichlitheradius-0165 5;,

phaseropposing relation to the waves reflected from the other.

curvature of the bends was 4 inches,- .all..'other. conditions being thesame, the measured phase displacement was degrees. *Iir-beth 'cases the'plane of polarization of the incident waveswas at-- an angle of 45degrees to the YZ plane. Inasmuch as the diiierenceinphase isattributable to the difierence in the velocity with which the twocomponents are propagated throughthe"' bend, it is recognized that byproper'choice .of.

operating frequency and/or dimensions, the phase v -a multiple thereof.

displacement may be made 180' degrees or.a multiple thereof. In suchcase,. the 'plane of polarization of the emergent waves might be.displacedbut it would'be invariable and elliptical polarization would beavoided. This condition" o in'a hollow pipe gu1d'e'of rectangularcross-sec would obtain, however, only for a particular operatingfrequency andnot for any considerable range of frequencies, and itwouldimpose a re.- striction on the radius of curvature or length'of thebend; It. is to .be noted,-too,. that. if a bend' ss.

causes'elliptical. polarization, the effectis;no.t"' cancelled, butdoubled, by refiectingthe emergent; waves or otherwise vcausingthem totraverse the same bend in the oppositedirection:

I'have discoveredlithat' the second bend I3" 40 largely compensates for.the deleterious effects introduced by the first bend I I7.lvioreparticularly I have found that" with. the. two bends arranged":in'the manner herein described; a plane polarized H11 waveenteringthroughguide section I I at'any section-and 1t 1s associatedwitlrn'reans; *notillu'sangle of'polarizationemerges through guidesection 14 with substantially no evidence of "elliptical? polarization.This .is .ta'kento mean that the" I phase displacement introducedi'bythe second bend. issubstantially equaliandopposit'e to the phasedisplacement. introduced lbythe first bend; The, two bends maythereiorebe said toshave' substantially the, same phase length; Inexplanation. of' these observationsit'imaybe noted that if the wavepassing through guide-section II is polarized at an angle of 45Tdegreeswith respect to the YZplane, it may be regarded. as comprising. twoequal components, one in the plane of the..bend and'oneat right anglesthereto, and" that the two components are Subjected to sub-. 60,

stantiallythe same treatment in passing through. the pair. of. bends;That; is, each component". passes through one bend with its. electric.vector in the plane of the bend and it passes through theother bendwithitsele'ctric. vector normalto;

the .plane thereoflj Inv short, the ele'ctricalflengthif of the pair. ofbends appears thesame .t'o the two:

components and they. emerge withjno phasedif-L' ference between them..Forptheir'angls of'polarization of the appliedxwaves the. ttvocompo-7o, p

' a wave-tight 'rotary'jointor 'swivel, which 'may"' nents are not sonearly equal and -the efifct.de scribed therefore obtains. to alesserextent; but" with the v.electridvector. =more nearly. coincident v with.or. normalto the .plane..of;.the bends,..the latter. havealessertende'ncy .to split. theappliedgm waves into phase displacedcomponents. In view of the foregoing explanation it will be understoodthat the phase compensation obtaining in the Fig. 1 system is notcritically dependent on the operating frequency and that the arrangementis efiective to suppress elliptical polarization over a wide range offrequencies- Partial reflection" of the-transmitted waves is anotherundesirable effect that is attributable to asingle Wave guide bend, forthe bend tends to introduce an impedance discontinuity in the thatfthewaves reflected from the one are in The two bends in Fig. 1 constitute apair 'of =sucli discontinuities, and they ,may. be advantageously spacedapart in reflection-canceling relation. In the specific embodimentdescribed with reference to Fig. 1, a spacing Lofabout'l incheswasfoundt'dyi'eldminimum reflection losses. Theoretical considerations'imdicate that the optimum spacing isapproximatel'y 1' one-half of" thewavelength "within" the: guide; or

Fig. 3 is a cross-sectional view of one-'of'the bends I0; I3 taken inthe planeof the bend? The radius R indicates themean radius'of'curvature. Fig. 3 is equally illustrative of "an" arcuate-bend tion. Theamount of reflectionloss that'occurs" within such a bend ismarked-lrdepen'dent on the arcuate length of the bendor, in otherwordsy'on" the mean-radiusofcurvature R: It'is found=that" 'the'opti'mumarcua'te length 1rR/2-fo'r minimum internal reflection lossesiscriticalIy' dependent on'the wave-'fi' 'equency'andis approximatelyequal to a half wavelength'or multiple'thereof'.

Fig. 4 illustrates diagrammatically a" radio "transmitting and/orreceiving system embodying? the present invention; The-system comprisesva horizontally-aimed paraboloidal reflector 2D "that is fixedly attachedto" the vertically disposed-hot low pipe guide I I. The guide is ofcircular-cross tratedffor' rotating'it about its-axis. At it'supper"extremityguide I I is terminated "by the" double bend structure-'ofFig.1} the latter being-disposed with guide section I2 norma'l to-the-axis"of theparaboloid and-with guide section I4 aligned with the-*axis ofthe-reflector 20." The en'd of guide section "l'd 'is open and it isdisposed" at' the; principal focus of 'the parab'oloid. In transmitting-guided waves issuing from-theopen end of section I4 strikethe--refiector wand form an'axiallydirected radio beam'." Fig.3'1" of U.S. Patent No; 2",'206,-92'3,--'issued'- July 9; 1940, to G; C.Southworth illustrates a 1 device which can be employed-forthis purposewhen the "transceiver 23 is to-be'used 'to'launcl'i waves-intotheguidefor transmission therethr0ug-h:- In receiving, radiowavesincident'upon the reflector aredirected to the open end-and" giverise-to guided waves inthe hollow 'pipeguide I I". Fig. -'12:"of-"UfSiP'atenir No." 2,257,783, issued October 71194-1; to A? E? Bowenillustrates a 1 device'- which can" be-employed for" this purposewhenthe transceiver 23 istobe used to receive'waves incident upontheguide."

The lower end of guide-'1 I "is connected through be of the known typerepresented schematically. by ya-.pair .of spaced conductive flanges .2I to a. stationary hollow. nipes uide'. 22;..th'at; leads .to....,transceiver..2.3 Theetransceiverjfiiis.adapted launch waves of the H11type into the lower end of guide 22 or to receive waves of that typefrom the guide, and in either case the orientation of the waves relativeto the guide is fixed or predetermined. The Fig. 4 system is adaptedprimarily for radio echo ranging or object locating and for this fieldof use the transceiver 23 may be assumed to transmit the waves in theform of short spaced pulses and to receive selectively the pulse echoesthat result from reflection of the waves at a distant object. Continuousrotation of the guide H and reflector 20 permits the entire horizon tobe kept under observation.

It is to be noted that in the normal operation of the Fig. 4 system, asabove described, the electric vector of the transmitted waves in guidell rotates continuously relative to the guide as the structure rotatesabout the vertical axis, or inasmuch as the field is non-symmetric itsuffices to say that the waves so rotate. Hence, if the vertical guide Il and guide section M were joined by a single 90-degree bend, thedirection of the electric vector would continuously vary with respect tothe plane of the bend and, intermittently, the waves would becomeelliptically polarized, that is, whenever the rotating structure passedthrough certain angular positions. The double bend provided in Fig. 4,however, substantially suppresses elliptical polarization as describedwith reference to Fig. 1 and by virtue of the spacing of the bendsminimum reflection losses are obtained regardless of the angularposition of the rotating structure. It may be noted also that thedirection of polarization of the radiated waves depends on the azimuthalangle of the rotating structure, and more particularly that withcontinuous rotation the radiated waves vary cyclically betweenhorizontal and vertical polarization. The direction of polarization ofthe received reflected waves varies in the same manner, but. theorientation of the waves appearing in guide 22 is neverthelessinvariable. Where two distant stations differ on azimuth by 90 degrees,it is accordingly possible to employ vertically polarized waves forcommunicating with the one station and, merely by rotating the antennasystem, to shift to horizontal polarization for communication with theother.

A feature of the Fig. 4 system is that with ellipticity of polarizationsubstantially eliminated in the manner described, it is possible toemploy a swivel joint of the simplest time. It is not necessary, forexample, to employ a joint that is adapted to convert the H11 wave to asymmetric type of wave for the purpose of coupling the stationary androtating guide sections.

Although the present invention has been described with reference tospecific embodiments thereof, it will be appreciated that the inventionis susceptible of embodiment in other forms within the spirit and scopeof the appended claims.

What is claimed is:

1. A microwave transmission system comprising a hollow-pipe guide andmeans for transmitting waves of non-symmetric type through said guide,said guide having two adjacent, substantially identical bends fixed inmutually perpendicular planes.

2. A microwave transmission system comprising a hollow-pipe guide ofsubstantially circular cross-section and means for transmitting waves ofdominant type through said guide, said guide having a pair of adjacentarcuate right angle bends that are of substantially equal phase lengthand are fixed in mutually perpendicular planes whereby said bends havesimilar but opposite effects with respect to the production ofelliptical polarization of said waves.

3. A microwave transmission system comprising a hollow-pipe guide ofsubstantially circular cross-section and means for transmitting waves ofdominant type through said guide, said guide having a pair of similarright angle bends spaced apart an approximately integral multiple ofhalf wavelengths in reflection cancelling relation to each other, therespective planes of said bends being mutually perpendicular.

4. In combination, a hollow-pipe guide for the transmission ofultra-high frequency electromagnetic waves, said guide being ofsubstantially circular cross-section and having a first smoothly curvingbend therein, means for applying to said bend for transmissiontherethrough polarized waves the field of which is subject to rotationrelative to the guide, said guide having a second similar bend ofsubstantially the same phase length adjacent the first bend, and saidsecond bend being fixed in a plane that is substantially perpendicularto the plane of the first bend.

5. In combination, a hollow-pipe guide for the transmission ofultra-high frequency electromagnetic waves, said guide being ofsubstantially circular cross-section and having a first substantiallyarcuate right angle bend therein, means for transmitting through saidguide electromagnetic waves the polarization of which is subject tovariation with reference to the plane of said bend, said guide having asecond substantially identical bend adjacent the first bend, and the twobends being fixed in planes that are sub stantially perpendicular toeach other.

6. In combination, a hollow-pipe guide of substantially circularcross-section for the transmission of ultra-high frequencyelectromagnetic waves, said guide having a bend therein such as toproduce elliptical polarization of the transmitted waves, meanscontinually changing the orientation of the transmitted waves withreference to the plane of said bend whereby the degree of ellipticityintroduced by said bend continually changes, and means for substantiallyneutralizing the variable effect of said bend on the transmitted wavescomprising a second bend in said guide adjacent said first-mentionedbend, said second bend being of substantially the same phase length asthe first-mentioned bend but disposed in a different plane.

7. In combination, a hollow-pipe guide, means for rotating said guideabout a longitudinal axis, means at one end of said guide for launchingplane polarized waves into said guide for transmission therethrough orfor receiving such waves from said guide, a pair of substantially equalarcuate bends of substantially the same phase length adjacent each othernear the other end of said guide, said other end being open for theradiation or interception of radio waves and said bends being fixed inmutually perpendicular planes.

8. In combination, a vertically disposed hollowpipe guide 'ofsubstantially circular cross-section, said guide having at its upper enda pair of substantially identical right angle curving bends fixed inmutually perpendicular planes and an opening for the radiation orinterception of radio waves, means for rotating said guide about avertical axis, and means at the lower end of said guide for launchingtherein or receiving therefrom guided electromagnetic waves of thedominant type.

- 1 t 9; .In* combination, ae'section of: :hollowepipe V iguideintherformiof"twozsuccessive :curved' bends of substantially equallphaselength: fixedzinrsubstantially; mutually perpendiculariplanes,transiceiver. means forexciting:electromagnetic waves inrsaid guide fortransmission throughisaid bends in succession 'or forereceivingelectromagnetic of similar adjacent bends in respective'planes thataresubstantially perpendicular" to each other; said bends being spacedaapartvan approximately integral multiple of half Wavelengths insubstantially refiectiomcancelling relation to each other.

13; A microwave transmissionsystem comprising atubular uniconductor'wave guidingpassage having a pair of similar adjacent bends ofsubstantially equal phase lengthifixed in respective planes "that aresubstantially perpendicular" to each othenand .means'for exciting in oneend i of said pair of bends a non-symmetric plane polarized wave theorientation of'which is variable relative to the plane of the bendnearestsaid :one

end. V

14. A'microwave transmission system compris iing a tubular uniconductorwave guiding passage .-:having a pair of adjacent bends of'substantially .equal phaselength; fixed'in planes ithat aresubstantiallyperpendicularto each other, means including a:wavetransceiver for. applying to or receiving from one end of saidupair ofbends a nonsymmetricplaneupolarized electromagnetic wave, and meansforrotating said passage about a'lonigitudinal axis-passinglthrougn saidone end.

. 15. A microwave transmission system comprising a tubular:.uniconductorWave-guiding pasisagehavinga-pair'of adjacent, substantially identicalbends of substantially"equalphase length fixed in respective "planes 1that are substantially perpendicular to *each other, and transceivermeans ior applyingtto ortreceivin'g from one end of said pair of bends anon-symmetric plane polarized .wave that rotates :continuously withrespect to the said end.

-=WARREN A. TYRRELL.

: REFERENCES CITED "Thefollowingreferencesare of record inthe file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,129,669 I Bowen Sept. 13, 19382,129,712 Southworth Sept. 13, 1938 2,206,923 Southworth July 9', 19402,398,095 7 Katzin "Apr. 9, 1946 2,407,305 Langstroth "Sept. 10, 19462,410,827 Langstroth Nov. 12, 1946 "2,412,320 Carter Dec. 10, 19462,416,675 Beck et a1 Mar. 4, 1947 I OTHERREFERENCES "Proceedings of TheInstitute of Radio Engineers, vo1. 24,-"No'2-10, October 1936 (pages1325- 1328).

